CHAPTER 15 VFD CONTROLLER/DRIVER
326
User’s Manual U11302EJ4V0UM
15.10 Calculating Total Power Dissipation
The total power dissipation of the
µ
PD780208 Subseries is the sum of the values of the following three
parts. Design your application set so that the sum is lower than the total power dissipation P
T
stipulated
in
Figure 15-22
. (The recommended operating condition is 80% or lower of the rated value.)
<1> CPU: The power consumed by the CPU and calculated with V
DD
(max.) x I
DD
(max.)
<2> Output pins: The power dissipation when the maximum current flows through the display output pins
<3> Pull-down resistors: The power consumed at the on-chip pull-down resistors connected to the display output
pins
Figure 15-22. Allowable Total Power Dissipation P
T
(T
A
= –40 to +85
°
C)
The following example assumes the case where the display examples shown in
15.9
are displayed.
15.10.1 Segment type (display mode 1: DSPM05 = 0)
The calculation method for the total power dissipation in the case of the display example in Figure 15-23 is
described below.
Example
Assume the following conditions:
V
DD
= 5 V
±
10%, 5.0 MHz oscillation
Supply current (I
DD
) = 21.6 mA
Display output: 11 grids
×
10 segments (cut width = 1/16: when DIMS1 to DIMS3 = 000B)
Maximum current at the grid pin is 15 mA.
Maximum current at the segment pin is 3 mA.
At the key scan timing, display output pin is OFF.
Display output voltage: grid
V
OD
= V
DD
– 2 V (voltage drop of 2 V)
segments V
OD
= V
DD
– 0.4 V (voltage drop of 0.4 V)
Fluorescent display control voltage (V
LOAD
) = –35 V
Mask option pull-down resistor = 25 k
Ω
800
600
400
200
–40
0
+40
+80
Temperature [
°
C ]
Power dissipation P
T
[mW]
Содержание mPD780204
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